Seen in the qtdeclarative textalignment example (examples/qtquick/righttoleft/textalignment/textalignment.qml

The example has bidi text with an italic font. The default font doesn't have italic glyphs for the characters and so additional font engines are being loaded to find one that does, for every character it appears which is increasing the time the example takes to load significantly.

Caching all font engines once loaded isn't the answer but maybe there's a way limit the number tried and/or shortcut to one already loaded for repeated misses.